This disclosure relates to positive displacement pumps, and more particularly to a high-pressure to low-pressure changeover valve for a positive displacement pump.
A standard air operated diaphragm pump (AODD) utilizes a single housing, dual diaphragms, and compressed gas to drive a process fluid through the pump. In an AODD, two fluid displacement members, typically diaphragms, are joined by a shaft, and compressed gas is the working fluid in the pump. Compressed gas is applied to one of two pumping chambers, associated with the respective diaphragms. When compressed air is applied to the first pumping chamber, the first diaphragm is deflected into the first fluid cavity, which discharges the process fluid from that fluid cavity. Simultaneously, the first diaphragm pulls the shaft, which is connected to the second diaphragm, drawing the second diaphragm in and pulling process fluid into the second fluid cavity. Delivery of compressed gas is controlled by a valve, and the valve is usually actuated mechanically by the diaphragms. Thus, one diaphragm is pulled in until it causes the actuator to toggle the valve. Toggling the valve exhausts the compressed gas from the first pumping chamber and introduces fresh compressed gas to the second pumping chamber, thus causing a reciprocating movement of the respective diaphragms. Alternatively, the first and second fluid displacement members could be pistons instead of diaphragms, and the pump would operate in the same manner.
A high-pressure AODD operates similar to a typical AODD, but it has an additional diaphragm and two additional pumping chambers. In a high-pressure AODD, a second housing is attached to the first housing, with a central diaphragm disposed between the two housings. A high-pressure AODD has four pumping chambers and three diaphragms. During a first stroke compressed gas drives the first diaphragm and the central diaphragm towards the first fluid chamber, providing twice the output pressure of a standard AODD. On the reverse stroke, compressed gas drives the second diaphragm and the central diaphragm towards the second fluid chamber.